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AQUATIC RESEARCH & SCIENCE COMMUNICATION CONSULTANTS
Heavy Metals in Fish and Shellfish
EOS Ecology Report No: 08002-ENV01-03 | July 2012Prepared for: Environment Canterbury
Prepared by: EOS Ecology; Shelley McMurtrie Reviewed by: Alex James
2012 SURVEY
E C O L O G Y
Report No. 08002-ENV01-03 July 2012EOS ECOLOGY | AQUATIC RESEARCH & SCIENCE COMMUNICATION CONSULTANTS
20-07-12
EOS Ecology or any employee or sub-consultant of EOS Ecology accepts no liability with respect to this publication’s use other than by the Client. This publication may not be reproduced or copied in any
form without the permission of the Client. All photographs within this publication are copyright of EOS Ecology or the credited photographer; they may not be used without written permission.
EOS ECOLOGY | AQUATIC RESEARCH & SCIENCE COMMUNICATION CONSULTANTS Heavy Metals in Fish and Shellfish 2012 Survey
HOW DO HEAVY METALS GET INTO OUR RIVERS AND ESTUARIES? 2
Heavy Metals Tested 3
WHERE WE SAMPLED 4
HOW WE SAMPLED 5
Shellfish 5
Estuary Fish and Shrimp 6
Freshwater Fish 7
OUR FINDINGS 8
Shellfish 8
Fish and Shrimp 10
DISCUSSION 12
The Christchurch 2011 Earthquakes 12
The Influence of Site Location 13
The Influence of Life History 15
Are Fish and Shellfish Safe to Eat? 16
ACKNOWLEDGEMENTS 17
REFERENCES 17
Report No. 08002-ENV01-03 July 2012EOS ECOLOGY | AQUATIC RESEARCH & SCIENCE COMMUNICATION CONSULTANTS
2
Christchurch, Canterbury
HOW DO HEAVY METALS GET INTO OUR RIVERS AND ESTUARIES?Heavy metals such as cadmium and lead, and metaloids like arsenic,
are found naturally in the environment. They are stable and cannot be
degraded or destroyed, so they tend to accumulate in soils, water, and
the atmosphere. We absorb tiny amounts of some heavy metals from
our food, drinking water, and the air. These very low levels generally
have no adverse effect, and in some cases can be beneficial—for
example tiny amounts of zinc and copper are essential to maintain
the metabolism of the human body. However, human activities from
industry and run-off from urban and agricultural landuse increase
the concentrations of these metals in the environment, potentially to
levels which could have adverse effects on humans and animals. Small
children and infants are more susceptible to ingesting high levels of
heavy metals as they consume more food per kilogram of body weight
than adults. The toxic effects of certain heavy metals can be particularly
detrimental to children’s developing organs, especially the brain.
Many heavy metals enter rivers in run-off from roads, factories
and agricultural land, and are usually directed to rivers through
the stormwater network. Once in the rivers they can accumulate
in the sediment. Eventually they get transported down-river to an
estuary, which traps the river sediment and thus accumulates metal
contaminants. This means that the sediment in rivers and estuaries
can have high contamination loads of heavy metals. The metal
concentrations vary by site depending on where contaminated sediment
is accumulating.
In general marine and freshwater organisms accumulate
contaminants from their environment and have been used extensively
to monitor heavy metal pollution. Shellfish feed by filtering particles out
of the water and often accumulate contaminants. This can have a direct
impact on our health if we eat shellfish that have high heavy metal
concentrations (e.g., above the safe limits set in the Australia New
Zealand Food Standards Code (FSANZ, 2008)) or that are contaminated
by bacteria or viruses. Many signs have been erected around the Avon-
Heathcote Estuary/Ihutai warning the public about eating shellfish due
to the potential for contamination from the discharge of treated sewage
(which ceased in March 2010) and stormwater inputs. Estuary and
freshwater fish may also accumulate heavy metals, potentially making
them unsafe to eat. Lead, mercury, and cadmium can be present in
fish naturally at low levels, or at higher levels as a result of pollution.
Mercury also bio-accumulates, meaning that animals further up the
food-chain also accumulate the mercury in the smaller animals that
they eat.
EOS ECOLOGY | AQUATIC RESEARCH & SCIENCE COMMUNICATION CONSULTANTS
3
Heavy Metals in Fish and Shellfish 2012 Survey
HEAVY METALS TESTED
MERCURY
Mercury occurs naturally in the environment but can also be released
into the atmosphere through industrial pollution. It can be transported
over large distances and as it has a long life can accumulate in the
environment when deposited into surface waters and soils. It is
present in fish and seafood products mostly as methylmercury (ENHIS,
2007). Methylmercury accumulates as smaller animals are eaten by
bigger animals, so animals higher up the food chain tend to have the
highest levels. High amounts of mercury can damage our kidneys and
central nervous system which can cause memory loss, slurred speech,
hearing loss, lack of coordination, loss of sensation in fingers and toes,
reproductive problems, coma, and possibly death (Vannoort & Thompson,
2006). The developing brain of a foetus is especially sensitive.
CADMIUM
Cadmium occurs naturally in low levels in the environment and is also used
in batteries, pigments, and metal coatings. Volcanic activity, industrial
processes such as smelting or electroplating, and the addition of fertilisers
can increase the concentration of cadmium in the environment. Shellfish
can also be high in cadmium (Gray et al., 2005; WHO, 1992). Long-term or
high dose exposure to cadmium can cause kidney failure and softening of
bones (Vannoort & Thomson, 2006), and high levels of cadmium have been
linked to prostate cancer (Gray et al., 2005).
LEAD
Lead is used in batteries, solder, ammunition, devices to shield x-rays,
and is found in most consumer electronic items. Most exposure to
humans is due to pollution, particularly from lead-based paint and
leaded fuel, both of which are no-longer used in New Zealand.
Lead can build up in the body and affects the nervous system,
reproductive system, and kidneys. Lead can be stored in bones without
harm but if calcium intake increases, the lead will be released from
the bone. Children and babies are particularly at risk from damage to
their central nervous system, which can cause learning difficulties and
behavioural changes. In New Zealand the estimated dietary exposure to
lead has been decreasing over time and in general our weekly exposure
to lead via our diet is under the guidelines developed by the World Health
Organisation (WHO, 2000).
Hg Pb
AsCd
For more information on arsenic see http://www.foodsmart.govt.nz/whats-in-our-food/chemicals-nutrients-additives-toxins/specific-foods/arsenic/
Maximum allowable levels of metal contaminants in food (FSANZ, 2008)
Metals (mg/kg) Crustacea Fish Shellfish
Mercury 0.5 0.5 0.5
Cadmium n/a n/a 2
Lead n/a 0.5 2
Arsenic (inorganic)* 2 2 1
*Inorganic arsenic is estimated to be 10% of total arsenic (USFDA 1993).
ARSENIC
Arsenic is a naturally occurring element that is common in soils, water,
and living organisms. In New Zealand arsenic levels in the environment
can increase as a result of mining, geothermal production, treated
timber, and erosion caused by intensive land use.
Fish and seafood can accumulate considerable amounts of organic
arsenic from their environment, but most foods contain tiny levels of
organic arsenic and occasional consumption is not a health concern.
An acute high level exposure to arsenic can lead to vomiting, diarrhoea,
anaemia, liver damage, and death. Long term (chronic) exposure is
thought to be linked to skin disease, hypertension, some forms of
diabetes, and cancer (Centeno et al. 2005). Arsenic is present in our
food in different chemical forms, but inorganic arsenic is more toxic
than organic arsenic. Most arsenic in our diet is present in the less toxic
organic form (for example fish and shellfish mainly accumulate organic
arsenic from their environment; WHO, 2011), and most of this leaves the
human body within several days. There is no regulatory limit for total
arsenic in fish or shellfish. However, it is difficult to reliably measure the
forms of arsenic that are present, so many surveys of arsenic content
measure total arsenic levels.
Hg
Pb
As
Cd
The Food Standards Code for Australia and New Zealand (FSANZ, 2008), has set maximum levels for the heavy metals mercury, lead, cadmium and
arsenic in our food. These limits are designed to ensure public health and safety when eating.
Report No. 08002-ENV01-03 July 2012EOS ECOLOGY | AQUATIC RESEARCH & SCIENCE COMMUNICATION CONSULTANTS
4
WHERE WE SAMPLED
Estuary fish (sand founder and yelloweye mullet) were collected within
the estuary from near the former discharge point of the Bromley
Wastewater Treatment Plant (WTP) and from the western side of the
Southshore spit. The WTP discharge was operating from the 1970s
through to March 2010, with treated wastewater now being discharged
directly to the ocean via a 3.2 km pipe out from Southshore Beach.
Cockles were collected in these two areas as well as at the southern
end of the causeway by Beachville Road, which is a popular shellfish
gathering site. Pipi were collected near the end of the Brighton Spit and
close to the estuary mouth, while estuary shrimp were collected from
the southeastern end of McCormacks Bay. Shortfin eels were collected
in the Avon River downstream of Anzac Drive, and in the Heathcote
River just downstream of Opawa Road. Whitebait were collected at
popular whitebaiting locations. For the Avon River this was opposite
Brooker Avenue, while in the Heathcote River this was in Opawa,
downstream of Brougham Street. Figure 1 shows these locations.
Cockles
Pipi
Shrimp
Mullet
Flounder
Whitebait
Eels
Avon River
Avon River
Discharge
Causeway
Plover St
Estuary Mouth
Southshore
Discharge
McCormacks Bay
Heathcote River
Heathcote River
FIGURE 1:
Locations where fish, shellfish
and shrimp were collected in
the 2012 survey
EOS ECOLOGY | AQUATIC RESEARCH & SCIENCE COMMUNICATION CONSULTANTS
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Heavy Metals in Fish and Shellfish 2012 Survey
HOW WE SAMPLED
SHELLFISH
Cockles (Austrovenus stutchburyi) and pipi (Paphies australis) were
collected at low tide by hand; pipi on the 23 February and cockles on
the 6 March 2012. The shellfish were kept cool with ice packs, their
length measured, and then delivered live to Hill Laboratories for heavy
metal testing. Ten replicate samples per site were collected. For cockles
each sample was made up of three specimens, while for the smaller
pipi seven specimens were needed per sample. Each sample was tested
by the laboratory for mercury, and five samples per site for arsenic,
lead, and cadmium.
Collecting cockles Collecting pipi
Measuring cockles in the laboratory Pipi
Report No. 08002-ENV01-03 July 2012EOS ECOLOGY | AQUATIC RESEARCH & SCIENCE COMMUNICATION CONSULTANTS
6
ESTUARY FISH AND SHRIMP
Sand flounder (Rhombosolea plebeia) and yelloweye mullet (Aldrichetta
forsteri) were collected from the two estuary fish sites over several days
in February and March 2012. Sand flounder were caught using a rigid
frame benthic drag net (mesh size 25 mm) that was set and dragged
behind the boat. Half a dozen drags per site were needed to capture
the required number of fish. A fine mesh (38 mm) gill net was used to
catch yelloweye mullet. Set netting is no longer allowed in the estuary
and so the gill net was instead deployed for less than ten minutes at
a time, with the boat and burley used to drive or attract fish into the
net. This was supplemented by fishing rods with six hook herring jigs to
capture mullet.
At each site ten fish of each type were placed on ice, anaesthetised
and measured in the lab, and delivered to Hill Laboratories for testing.
Ten fish of each type were analysed for mercury and five for arsenic
and lead. The small size of the flounder meant that two fish had to be
combined to make a single sample with sufficient flesh for testing in
two samples from the Discharge site and one from the Southshore site.
Shrimp (Palaemon affinis) were caught on the 4 April 2012 using
a fine mesh hand net and ten samples weighing approximately 6–10 g
each (wet weight) were delivered to Hill Laboratories for testing. All of
these samples were tested for mercury and five samples were tested for
arsenic and lead.
Pulling up the rigid frame benthic drag net used to capture sand flounder
Sand flounder
Catching shrimp in McCormacks Bay
Measuring a sand flounder
Yelloweye mullet
Shrimp
EOS ECOLOGY | AQUATIC RESEARCH & SCIENCE COMMUNICATION CONSULTANTS
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Heavy Metals in Fish and Shellfish 2012 Survey
FRESHWATER FISH
Shortfin eels (Anguilla australis) were collected from the Heathcote
River and Avon River using fyke nets that were baited and set
overnight on the 20 February 2012. These nets are a series of hoops
connected by mesh. Once the fish enter the inverted funnel entrance
they can’t find the narrow exit and are trapped. The next day the eels
were anaesthetised, their length measured, and either taken to Hill
Laboratories for analysis or returned live to the river if too many were
caught. Mercury levels were tested in ten eels and arsenic and lead in
five eels from each site.
Whitebait (most likely Galaxias maculatus) were collected during the
whitebaiting season, in October 2011, when the tiny fish are migrating
upriver after having spent six months developing in the ocean. Due to
sewage inputs into the rivers from sewerage pipes damaged during the
2011 Christchurch earthquakes, whitebaiting on the Avon and Heathcote
Rivers was less popular during this season. Whitebait on the Avon River
were therefore caught using hand-held nets while whitebait on the
Heathcote River were obtained from a whitebaiter who gave us a portion
of their catch. Ten samples from each site, weighing approximately
4 g and made up of 10–12 fish, were delivered to Hill Laboratories for
testing. All of these samples were tested for mercury and five samples
per site were tested for arsenic and lead.
Setting a fyke net in the Heathcote River
Shortfin eels caught in a fyke net
Report No. 08002-ENV01-03 July 2012EOS ECOLOGY | AQUATIC RESEARCH & SCIENCE COMMUNICATION CONSULTANTS
8
OUR FINDINGS
SHELLFISH
Where possible we collected larger shellfish; the size most likely to be
collected and eaten. Cockles, however, were smaller at the Southshore
and Discharge sites (average length of 38-39 mm compared to 50 mm at
the Causeway site), and the pipi found after an hour of searching were
not particularly large (average length of 47 mm) (Table 1).
Both pipi and cockles at all sites had levels of cadmium, lead, and
mercury below the Food Standards Australia New Zealand (FSANZ,
2008) maximum allowable level set for safe consumption of shellfish
(Figure 2). In fact, the average level of all three metals at each site was
at least 1/10 that of the FSANZ maximum allowable metal contaminant
levels. Cockles collected from the Discharge site had the lowest levels
of cadmium, and mercury, but had the highest levels of lead.
Arsenic was lowest in pipi at the Estuary Mouth and cockles at the
Discharge site, and highest at Southshore and Causeway sites. The FSANZ
(2008) provides guidelines for levels of inorganic arsenic in shellfish (as
well as in fish and shrimp). However, as this is difficult and expensive to
measure accurately, most studies measure total arsenic levels instead. In
America the US Food and Drug Administration (USFDA) has set maximum
allowable levels for total arsenic in shellfish at 86 mg/kg (USFDA, 1993).
The levels of total arsenic that we found in the estuary shellfish were much
lower than this, with the highest total arsenic level being 4.9 mg/kg in
cockles at Southshore, 3.9 mg/kg in cockles the Causeway site, 1.9 mg/
kg in cockles at the Discharge site, and 1.4 mg/kg in pipi near the Estuary
Mouth. Thus even the highest concentration of total arsenic was at least
1/10 that of the safe consumption levels set by the USFDA. The USFDA has
also conservatively set the inorganic arsenic component at 10% of total
arsenic (USFDA, 1993). If we apply this rationale to our samples then the
highest estimated inorganic arsenic levels would be 0.49 mg/kg; still below
the FSANZ guidelines of 1 mg/kg inorganic arsenic.Cockles collected from near the Causeway
EOS ECOLOGY | AQUATIC RESEARCH & SCIENCE COMMUNICATION CONSULTANTS
9
Heavy Metals in Fish and Shellfish 2012 Survey
TABLE 1: Average shell length (mm ± 1 std error) of shellfish collected in
March 2012
Cockles
Causeway 48 ± 0.4
Discharge 38 ± 0.3
Southshore 34 ± 0.4
Pipi Estuary Mouth 54 ± 0.6
0.00
0.01
0.02
0.03
0.04
CADMIUM
(mg/kg)
FSANZ guidelines for unsafe levels: above 2.0 mg/kg
Causew
ay
Discha
rge
Souths
hore
Estua
ry Mou
th
0.00
0.01
0.02
0.03
0.04
MERCURY
(mg/kg)
FSANZ guidelines for unsafe levels: above 0.5 mg/kg
Causew
ay
Discha
rge
Souths
hore
Estua
ry Mou
th
0.00
0.05
0.10
0.15
LEAD
(mg/kg)
FSANZ guidelines for unsafe levels: above 2.0 mg/kg
Causew
ay
Discha
rge
Souths
hore
Estua
ry Mou
th0
1
2
3
4
5
ARSENIC
(mg/kg)
USFDA estimated guidelines for
unsafe levels: above 86 mg/kg (FSANZ
inorganic arsenic = 1.0mg/kg)
Causew
ay
Discha
rge
Souths
hore
Estua
ry Mou
thCockles
Pipi
FIGURE 2:
Heavy metal levels in shellfish (cockles and pipi) collected
from the Avon-Heathcoste Estuary/Ihutai in March 2012
Report No. 08002-ENV01-03 July 2012EOS ECOLOGY | AQUATIC RESEARCH & SCIENCE COMMUNICATION CONSULTANTS
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FISH AND SHRIMP
The size of yelloweye mullet caught in this survey (average length of 258 mm
across both sites) were generally larger than those caught throughout the
estuary in 2010 (Unwin & Hawke, 2011), and although there is no size or catch
limit for yelloweye mullet, the larger size of fish we caught would be more
desirable for consumption (Table 2). The size of sand flounder caught (average
length of 89 mm across both sites) were generally similar to those caught in
the low tide channels in 2010 (Unwin & Hawke, 2011), but are smaller than
what would be regarded acceptable for eating (Table 2). The shortfin eels
caught were of similar size between the two rivers (average length of 460 mm
for Avon River and 461 mm for Heathcote River). While we retuned the largest
eels to the rivers as they are an important part of the breeding population of
this slow growing species, the specimens retained for analysis were still of a
size that would be caught and eaten.
The levels of lead and mercury from flounder, mullet, eels, and
whitebait were all well below the maximum acceptable levels for eating fish
(FSANZ, 2008) (Figure 3). However, in general flounder had higher levels of
lead than any other fish, with an average level of 0.16 mg/kg compared to
less than 0.03 mg/kg in other fish. In contrast flounder had very low levels
of mercury, as did whitebait—with both species sometimes recording levels
below the detection limit of 0.01 mg/kg. Shortfin eels had the highest levels
of mercury (average of 0.05 mg/kg), followed by yelloweye mullet (average
of 0.03 mg/kg).
The safe limit for inorganic arsenic in fish is 2 mg/kg, so the estimated
level of inorganic arsenic (i.e., 10% of total arsenic) in sand flounder
(estimated average 0.102 mg/kg), whitebait (estimated average of 0.083
mg/kg), yelloweye mullet (estimated average of 0.047 mg/kg), and shortfin
eels (estimated average of 0.013 mg/kg) were all below this level. Of the
fish tested, sand flounder had the highest levels of total arsenic (average of
1.02 mg/kg) followed by whitebait (average of 0.83 mg/kg). Inanga whitebait Shrimp
While not regularly eaten now, the Palaemon shrimps of the Avon-
Heathcote Estuary/Ihutai were once a prized delicacy, with the ‘Redcliff
shrimps’ cooked and sent throughout New Zealand through to the 1930s
(McMurtrie & Kennedy, 2012). The levels of lead and mercury in shrimp
from McCormacks Bay were well below the FSANZ maximum metal
contamination levels for food—being 0.5 mg/kg for mercury (no levels set
for lead) (Figure 3). Levels of lead in shrimp (average of 0.07 mg/kg), while
low, were still second highest after sand flounder. Levels of mercury in
shrimp (average of 0.008 mg/kg) were at similarly low levels as that found
in sand flounder and whitebait.
Following the USFDA (1993) conservative estimate of inorganic arsenic
being 10% of total arsenic, the estimated level of inorganic arsenic in
shrimp (estimated average of 0.22 mg/kg) was also well below the FSANZ
2 mg/kg guideline for Crustacea. However, the total arsenic levels (average
2.22 mg/kg) was still more than two times that of the sampled fish (mullet,
flounder, shortfin eel, whitebait), and was marginally higher than the
levels found in pipi from Southshore and cockles from the Discharge site.
However, total arsenic levels in cockles from the Causeway and Southshore
sites (3.4 and 3.9 mg/kg) still remained higher even than shrimp.
EOS ECOLOGY | AQUATIC RESEARCH & SCIENCE COMMUNICATION CONSULTANTS
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Heavy Metals in Fish and Shellfish 2012 Survey
Length of fish taken
for analysis (mm)
Length of all eels caught
(mm)
Shortfin eel
Avon River462 ± 14
(caught 10)461 ± 20
(caught 35)
Heathcote River461 ± 20
(caught 10)494 ± 25
(caught 27)
Length of fish taken
for analysis (mm)
Length of fish in estuary (Unwin & Hawke 2011)
(mm)
Yelloweye mullet
Discharge279 ± 14
(caught 10)
Low tide channel trawl:
198 ± 6 (caught 18)
Beach seines: 75 ± 1
(caught 728)Southshore
240 ± 12 (caught 10)
Length of fish taken
for analysis (mm)
Length of fish in estuary (Unwin & Hawke 2011)
(mm)
Sand flounder
Discharge86 ± 4
(caught 12)
Low tide channel trawl:
88 ± 3 (caught 12)
Beach seines: 39 ± 1
(caught 147)Southshore
94 ± 5 (caught 11)
)kgg/m(MERCURY
FSANZ guidelines for unsafe levels:
above 0.5 mg/kg
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0.00
(mg/kg)
LEAD
FSANZ guidelines for unsafe levels:
above 0.5 mg/kg
0.5
0.4
0.3
0.2
0.1
0.0
(mg/kg)
ARSENIC
DischargeSouthshore
McCormacks BayAvon River
Heathcote River
FSANZ guidelines for unsafe levels: (inorganic
arsenic) above 2.0 mg/kg. Note however these results
are for total arsenic.
3.0
2.0
1.0
0.0
FIGURE 3:
Heavy metal levels in fish and
shrimp collected from the Avon-
Heathcoste Estuary/Ihutai and
main rivers in 2012 (Whitebait
collected October 2011)
TABLE 2:
Average length of fish (mm ± 1 std error) caught for testing in 2012 compared to
fish lengths in the wider area
Report No. 08002-ENV01-03 July 2012EOS ECOLOGY | AQUATIC RESEARCH & SCIENCE COMMUNICATION CONSULTANTS
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THE CHRISTCHURCH 2011 EARTHQUAKES
On 22 February and 13 June 2011, 6.3 and 6.4 magnitude earthquakes
in Christchurch caused substantial damage to the city’s sewerage
infrastructure. Over 60,000 m3/day of untreated raw sewage entered
the city’s rivers and estuary for one month after each event, with
discharges of 10-20,000 m3/day prior to sewerage repairs in November
2011. The collection of whitebait in October 2011 therefore occurred
while there was still a small discharge of raw sewage into the Avon
River (estimated at 8,654 m3/day in August 2011) and estuary (direct
discharges estimated 5,643 m3/day in August 2011) as a result of the
2011 earthquakes. In contrast the rest of the fish, shrimp and cockles
were collected in March-April 2011, approximately four months after all
raw discharges into the City’s rivers or estuary had ceased. Thus while
the discharge of treated wastewater ceased in March 2010, because of
the large volumes of raw sewage that entered the estuary in the nine
months following the February 2011 earthquake, the current survey is
more indicative of an estuary still impacted by sewage discharges.
Liquefaction mounds in the Estuary at Humphreys Drive, caused by the February and June 2011 earthqaukes
DISCUSSION
EOS ECOLOGY | AQUATIC RESEARCH & SCIENCE COMMUNICATION CONSULTANTS
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Heavy Metals in Fish and Shellfish 2012 Survey
THE INFLUENCE OF SITE LOCATION
Because shellfish are sessile (i.e., they live in the sediment and don’t
move around a lot) they probably provide the best opportunity to look at
differences between sites. CBD (1988) found that smaller cockles had
higher levels of heavy metals than larger ones, but we did not find this
to be the case. In fact we found that the largest cockles had the highest
levels of cadmium, but this may have been more due to site location, with
the Causeway site having the largest cockles. Our results therefore imply
that site location has a greater influence on heavy metal levels in cockles
than size does.
Our results showed that cockles from the Causeway and Southshore
sites had higher levels of cadmium, mercury and arsenic than those
from the Discharge or Estuary Mouth sites, while lead was higher in
cockles from the Discharge site. These patterns are similar to those
found in the 2010 survey. The pattern of higher lead levels in the western
side of the estuary is also the same as that found over 20 years ago by
the Christchurch Drainage Board (CDB, 1988). Because the levels of
cadmium, mercury, and arsenic have always been lowest at the Discharge
site it is possible that these contaminants originate from the rivers or
stormwater drain inputs rather than the (now decommissioned) sewage
discharge. The Causeway and Southshore sites are located close to
areas where a number of stormwater pipes discharge directly into the
estuary (Figure 4), and so may be more exposed to the contaminants in
the stormwater discharges than the Discharge site would be. This may
similarly mean that the higher lead levels at the Discharge site could be
an historic artefact of the discharge of treated wastewater from the City’s
wastewater treatment ponds, which discharged into the estuary at this
point between 1958 and 2010 (McMurtrie & Kennedy, 2012). The fact that
the lead levels remain high in cockles from this site despite the sewage
discharge having ceased since March 2010 may indicate that there is a
historic load held in the estuary sediments around this location. However,
FIGURE 4:
Small stormwater pipe discharges
(locations provided by Environment
Canterbury) into the Estuary in
relation to the location of the cockle
monitoring sites It is possible the
stormwater discharges near to the
Causeway and Southshore sites
contribute to the higher levels of
cadmium, mercury, and arsenic in
cockles from these sites compared to
the Discharge site
Old discharge point
Cockle collection site
Stormwater discharge
Discharge
Causeway
Plover St
Report No. 08002-ENV01-03 July 2012EOS ECOLOGY | AQUATIC RESEARCH & SCIENCE COMMUNICATION CONSULTANTS
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View of the estuary from Kinsey Terrrace, looking towards the oxidation ponds
sediment testing in 2011 indicated that total lead levels in sediment at
the Discharge site were little different to other areas around the estuary,
with the exception of the Avon River mouth (which had higher levels; EOS
Ecology, unpublished data).
For freshwater fish (whitebait and shortfin eels), the river that
they were collected from made little difference to the levels of mercury
or arsenic, with fish collected from both rivers having similar levels.
However, lead levels were only marginally higher in both whitebait and
eels caught in the Avon River. For the estuarine fish, there was also no
relationship between site and heavy metal contamination, with levels in
each fish species relatively similar between sites. The obvious exception
was the slightly higher levels of arsenic found in sand flounder collected
at the Southshore site. Given the transient nature of both types of fish
(but in particular yelloweye mullet) it is unlikely that any differences
would be associated with where they were caught.
Because fish move around so much it is difficult to attribute any
differences in heavy metal levels to the location where the fish were
caught. Although typically regarded as marine species, flounder and
mullet do not just live in the sea and estuary area, but move up into the
lower reaches of rivers to feed. Sand flounder will move a short distance
up-river, although they stay within the tidal zone. Yeloweye mullet
however, regularly move considerable distances up-river, into freshwater
above the tidal zone, where they may remain and feed for several tide
cycles before returning to the estuary. The whitebait caught would have
spent around six months developing in the ocean before their spring
migration into rivers and streams, where they will stay for 1–2 years
before moving down into the tidal reaches of rivers to lay their eggs in
grasses along the streambank during autumn high tides. When the young
hatch they are washed out to sea to develop and will return in the next
season’s whitebait run. In contrast eels will typically spend most of their
life in freshwater, only migrating to the sea to spawn later in their life.
EOS ECOLOGY | AQUATIC RESEARCH & SCIENCE COMMUNICATION CONSULTANTS
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Heavy Metals in Fish and Shellfish 2012 Survey
THE INFLUENCE OF LIFE HISTORY
Some of the differences in heavy metal loadings between the animals
collected may be due to differences in life history, habitat preferences,
feeding behaviour, and even how metals behave and accumulate, rather
than site-specific differences.
Feeding habitats and life history patterns could influence heavy
metal levels in fish. Sand founder live and feed from the estuary floor
and so may be more exposed to contaminants in the sediment than
other free-swimming fish such as mullet and whitebait. This could
explain the higher levels of lead in flounder compared to other fish. The
whitebait caught would be little more than six months old, with much
of this time having been spent in the ocean where they feed on tiny
zooplankton in the water. Thus heavy metal levels in whitebait could
be a reflection of their time spent at sea and in the estuary as much as
their time spent in the river.
The age of fish caught and their feeding habits could help explain
the level of mercury in fish, as it accumulates over an animal’s life
time as well as up the food chain (e.g., predators also accumulate the
mercury from the prey they eat). The much higher level of mercury
in eels than all other animals tested may be related to their age and
predatory status. The eels caught in this study could be somewhere
between 14 and 22 years (as they grow very slowly and are long-
lived) and would feed on smaller fish as well as invertebrates. The
bioaccumulation of mercury could also explain the higher levels in
yelloweye mullet compared to either whitebait or sand flounder. While
yelloweye mullet would not be nearly as old as the shortfin eels (the
mullet were estimated to be only 1-2 years old) their age and size is still
greater than that of sand flounder and whitebait, which were estimated
at around six months of age.
Pipi and cockles are relatively stationary animals that live in the
sediment and filter particles out of the water column. Compared to
fish, they actively ingest heavy metals bound to particles (organic
and inorganic), meaning that they would be more exposed to heavy
metals while feeding. Shrimp also feed by stirring the sediment up and
collecting very small particles of organic matter, and so they too would
be exposed to the heavy metals bound to this food. Our study and other
studies (FSA, 2005) have found that cockles accumulate more arsenic
than fish do. This may be due to their feeding or habitat preferences,
or other factors. The feeding habits of shrimp may also explain the high
levels of arsenic in them compared to the fish tested.
Shortfin eel in the Avon River
Report No. 08002-ENV01-03 July 2012EOS ECOLOGY | AQUATIC RESEARCH & SCIENCE COMMUNICATION CONSULTANTS
16
ARE FISH AND SHELLFISH SAFE TO EAT?
Cockles, pipi, shrimp, yelloweye mullet, sand flounder, shortfin eels,
and whitebait all had metal concentrations (e.g., mercury, cadmium, lead,
arsenic) below the FSANZ (2008) limits and so based on heavy metal
levels they are safe for consumption. However, the on-going high arsenic
levels in cockles and shrimp could warrant further investigation, with
testing of inorganic arsenic in cockles and shrimp to properly ascertain
the relationship between total arsenic and inorganic arsenic levels.
Despite this clean bill of health, the consumption of shellfish in
particular should still be cautioned. Bacteria (E. coli, Salmonella) and
enteric viruses (norovirus)—which can cause vomiting, diarrhoea,
and abdominal pain—are still being found in shellfish collected
from the estuary as a result of faecal contamination from either
human (sewage overflows) or wildlife (birds, dogs) sources. Quarterly
monitoring by EOS Ecology has shown that both E. coli and norovirus
concentrations at sites near to the Avon and Heathcote River mouth
dramatically increased after the February earthquake when there
were sewage overflows into the city’s rivers and estuary. Bacteria (E.
coli) concentrations increased to 16,000 MPN/100g (MPN stands for
‘most probable number’) and norovirus was detected at extremely high
concentrations (>10,000 genome copies/g shellfish digestive tissue).
While no specific microbiological guideline criteria exist for shellfish
gathered for personal consumption or non-commercial purposes, the
safe E. coli limits for commercial food set by the Australian New Zealand
Food Authority in 2011 is 700 MPN/100g in bivalves (FSANZ, 2011). The
levels recorded in cockles following the February 2011 earthquake were
far in excess of this level and they would have been dangerous to eat
raw or lightly cooked. These high levels also illustrate how responsive
shellfish are to bacterial and viral contamination in water.
The discharge of raw sewage into the City’s rivers and estuary Cockles being collected from the Estuary
ceased in November 2011, but there are still chances of further sewage
discharges as the City continues to repair its badly damaged sewerage
infrastructure. When these sewage overflow events occur the public
are being kept informed through warning signs and warning notices
on Environment Canterbury’s website. The CCC still maintains their
warning signs around the estuary advising against taking shellfish for
consumption. Once the sewerage network is repaired it is hoped that
the viral and bacterial levels in shellfish will drop.
Cockles
Pipi
Shrimp
Mullet
Flounder
Whitebait
Eels
Heavy metal concentrations safe
for eating?
EOS ECOLOGY | AQUATIC RESEARCH & SCIENCE COMMUNICATION CONSULTANTS
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Heavy Metals in Fish and Shellfish 2012 Survey
REFERENCESBatcheler, L., Bolton-Ritchie, L., Bond, J., Dagg, D., Dickson, P., Drysdale,
A., Handforth, D. & Hayward, S. 2006. Healthy estuary and rivers of the city: water quality and ecosystem health monitoring programme of Ihutai. Environment Canterbury, Christchurch City Council, and the Ihutai Trust, Christchurch. 56 pp.
Centeno, J.A., Gray, M.A., Mullick, J.G., Tchounwou, P.B. & Tseng, C. 2005. Arsenic in drinking water and health issues. In: Moore, T.A., Black, A., Centeno, J.A., Harding, J.S. & Trumm, D.A. (eds.). Metal Contaminants in New Zealand. Sources, Treatments, and Effects on Ecology and Human Health. Resolutionz Press, Christchurch. Pp 415–436.
Christchurch Drainage Board (CDB) 1988. Heavy metals in the rivers and estuaries of metropolitan Christchurch and outlying areas. Christchurch Drainage Board, Christchurch. 221 pp.
European Environment and Health Information System (ENHIS) 2007. Exposure of children to chemical hazards in food. European Environment and Health Information System, Fact Sheet No. 44, Code RPG4_Food_Ex1.
Food Standards Agency (FSA) 2005. Arsenic in fish and shellfish. Food Surveillance Information Sheet 82/05. 24 pp.
Food Standards Australia New Zealand (FSANZ) 2008. Australia New Zealand Food Standards Code (Incorporating amendments up to and including Amendment 97). Anstat Pty Ltd., Melbourne.
Food Standards Australia New Zealand (FSANZ) 2011. Australia New Zealand Food Standards Code – Standard 1.6.1 – Microbiological limits for food. Anstat Pty Ltd., Melbourne. Retrieved on 3 July 2011, www.comlaw.gov.au/Details/F2011C00582
ACKNOWLEDGEMENTSThank you to David Tattle (Pegasus Bay Trading) and Rennie Bishop
(Canterbury University) for their boat and expertise in collecting the fish
from the estuary. Comments on the draft report by Alex James (EOS
Ecology) and Lesley Bolton-Ritchie (Environment Canterbury; ECan)
were also appreciated.
This work was funded by ECan and contributes to the “Food Safe
to Eat” component of the “Healthy Estuary and Rivers of the City”
programme established by ECan, CCC, and the Avon-Heathcote Estuary
Ihutai Trust (Batcheler et al., 2006).
Gray, M.A., Harrins, A. & Centeno, J.A. 2005. The role of cadmium, zinc and selenium in prostate disease. In: Moore, T.A., Black, A., Centeno, J.A., Harding, J.S. & Trumm, D.A. (eds.). Metal Contaminants in New Zealand. Sources, Treatments, and Effects on Ecology and Human Health. Resolutionz Press, Christchurch. Pp 393–414.
McMurtrie, S. & Kennedy, S. 2012. Exploring an Estuary. A Field Guide to the Avon-Heathcote Estuary/Ihutai Christchurch. Avon-Heathcote Estuary Ihutai Trust, Christchurch. 50 pp.
Unwin, M. & Hawke, L. 2011. Assessment of fish populations in the Avon-Heathcote Estuary: 2010. National Institute of Water & Atmospheric Research Ltd, Christchurch, New Zealand. NIWA Client Report No: CHC2011-040. 26 pp.
United States Food and Drug Administration (USFDA) 1993. Food and Drug Administration. Guidance document for arsenic in shellfish. DHHS/PHS/FDA/CFSAN/Office of Seafood, Washington, D.C. Retrieved on 4 July 2011, www.speciation.net/Public/Links/DB/Links/detail.html?id=762.
Vannoort, R.W. & Thomson, B.M. 2006. 2003/2004 New Zealand Total Diet Survey: Agricultural compound residue, selected contaminants and nutrients. New Zealand Food Safety Authority. 144 pp.
World Health Organisation (WHO) 1992. Cadmium. Environmental Health Criteria No. 134. Geneva: World Health Organisation.
World Health Organisation (WHO) 2000. Evaluation of certain food additives and contaminants (53rd report of the Joint FAO/WHO Expert committee on food additives). WHO Technical Report Series, No 896. Geneva. World Health Organisation.
World Health Organisation (WHO) 2011. Guidelines for Drinking-Water Quality. 4th (ed). World Health Organisation, Geneva. 451 pp.
EOS ECOLOGY | AQUATIC RESEARCH & SCIENCE COMMUNICATION CONSULTANTS P: 03 389 0538 | F: 03 389 8576 | info@eosecology.co.nz | www.eosecology.co.nz | PO Box 4262, Christchurch 8140, New Zealand
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